Utterly predictable (as evidenced by the fact that I did predict it): three major advertising groups have announced that they will ignore the “Do Not Track” header, because of Microsoft’s decision to enable it by default in IE 10.

How could anyone have failed to see this coming? Advertisers were perfectly willing to honor DNT as long as it was enabled only by the small population of users who care about tracking cookies. Now (at least among IE 10 users) they’d be restricted to tracking only the even tinier population of users who actually volunteer for tracking cookies.

Unless Microsoft changes their decision, they will have effectively killed DNT. The only way to revive it would be to legislatively require that it be honored (and I fully expect Steve Gibson to endorse that approach). The result could fundamentally undermine the viability of current online advertising business models, which could put a lot of Web sites out of business — or force them behind paywalls.

I generally accept the premise that Microsoft is not run by idiots, so I’m baffled by why they would do this, when the consequences were so foreseeable. The only explanation I can think of sounds like a conspiracy theory: perhaps it’s all a ploy to undermine their biggest competitor, Google. Google has a lot more to lose than Microsoft, if advertisers are compelled to respect DNT. Perhaps they know that by forcing the issue, they’ll make legislative action more likely, and by making DNT the default, they’ll be taking money out of Google’s pocket.

At any rate, I’m just glad I don’t use IE. I like targeted advertising.